When the prologue ends and chapter 1 starts, break all the tombstones to earn:
Then, move the flowers in the flower basket to take the jewel in the gift box.
Go to the left and insert this jewel into the owl's eye socket, then enter the door that unlocks.
Collect the crank wheel, then attach it to the bottom of the pulley and click it. This reveals the cage, thus opening the curtain.